If you're thinking of taking someone to Philip Glass's Satyagraha, best not to let on that it's in ancient Sanskrit, with no surtitles. To be honest, it makes little difference, given that there's no narrative as such. The action, if one can call it that, concerns the years of spiritual preparation undergone by Mahatma Gandhi in South Africa at the turn of the 20th century.

An iconic figure who influenced him is silently featured in each of the acts: Leo Tolstoy, seen in an alcove high on the left, Rabindranath Tagore similarly on the right, Martin Luther King gesticulating on a podium in the centre. Mind-improving homilies are projected on the rear wall: “the wise should act” — that kind of thing. If you want to know what the sung text, derived from the Bhagavad Gita, is about, you could buy a programme. But it’ll cost you another £6 and won’t necessarily enlighten.

As for Glass’s music, it’s the usual triumph of banality: scalic figures running up and down, an oscillating motif, a motor rhythm, all scored with intermittent imagination. Few of these ideas are worth hearing more than once: after several dozen repetitions, you begin to enter the mindset of Gandhi who endured all manner of privations and torment for a great cause. But should we have to suffer too?

Alan Oke takes the role of Gandhi, easy to spot in his off-the-shoulder number. One of the sopranos sings horribly out of tune for quarter of an hour, but happily it’s impossible to identify her or any of the other characters. Stuart Stratford conducts patiently. The production, directed and designed by Phelim McDermott and Julian Crouch of Improbable, creates a ritualistic experience, demonstrates virtuoso stagecraft and strives heroically to fill in the gaps left by the opera itself.